how to make sure that the webservice is returning xml

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XML

i was told that the webservice returns xml, i also found it by writing
after creating proxy of that method , i wrote

DS.WRITEXML(PATH,XMLWRITEMODE.WRITESCHEMA);

now when i was tring to implement the same i am not getting
my webmethod is

[WebMethod]
        public string getdetails()
        {
            XDocument xd = XDocument.Load(@"D:\satish1\na.xml");
            var query = from p in xd.Descendants("item")
                        select new
                        {
                            name = p.Element("title").Value,
                            des = p.Element("description").Value
                        };
            return query.ToString();
ds=proxy.getdetails();

I am not getting this thing it is saying cannot convert string to system .data.dataset.can i di this in any way.plz help me